Two aspects of the etiology of hemorrhoids and anal fissures intersect in the rectal area of the anal canal, creating multiple injuries: anatomical factors on the one hand and fecal dynamics on the other. The recto-anal canal in its physiological state is funnel-shaped, with the anal canal (the portion from the anal verge to the superior plane of the anorectal ring) being the narrowest. The lumen of the anal canal is longitudinally fissured anteriorly and posteriorly in vivo; a mild physiological state of high outlet resistance exists when defecating in the physiological state. Normal stool is in a form between solid and fluid, and the forces on the soft tissues at the anal canal are multi-point, multi-directional, and vary in size, and are roughly of three types: (1) frictional forces. This force is the force of feces on the anal canal, the direction is downward, and its action points are almost extensive, but the friction at the three anal pads and the migrating epithelium of the anal canal on both sides is the largest. (2) Dilatation force. It is the force of feces acting horizontally at the anal canal, and both sides of the anal canal are subjected to the greatest dilatation force during normal defecation. (3) Thrust or/and impact force. The thrust force is the combined force of the expansion force and friction force of normal stool or dry stool in the downward direction; the impact force is the force of dilute stool on the soft tissues at the anal canal in the downward direction, most obvious at the three anal pads; it is expressed as a thrust force (long acting time) in normal stool and dry stool, and as an impact force (short acting time) in dilute stool; the size of this force has a positive correlation with the size of abdominal pressure. In case of changes in the nature of stool and frequency of defecation, the soft tissues of the anal canal will be damaged by the squeezing, friction, expansion, pushing and pulling of the stool, and there are four basic forms of such damage: (1) abrasion of the skin of the anal canal. (2) Anal canal soft tissue crush injury. (3) Anal canal skin laceration. (4) Anal canal skin pushing and pulling injury. The local bleeding, edema, hypertrophy or/and downward displacement of the anal cushion caused by the injury creates a pathological high resistance state of the anal canal exit. The aim of treatment is to relieve this pathological high outlet resistance state, so that the feces can be passed smoothly and the dynamic balance of the outlet mechanics can be achieved. The influence of fecal kinetic factors on the formation and treatment of hemorrhoids and anal fissures is discussed as follows.
1 The influence of fecal kinetic factors on hemorrhoids
1.1 External hemorrhoids
1.1.1 Thrombosed external hemorrhoids
The squeezing and pushing of the soft tissues at the anal canal by feces during defecation, especially below the dentate line, causes inelastic deformation and destruction of the fine subcutaneous blood vessels of the anus, resulting in vascular injury and bleeding and the formation of subcutaneous hematomas at the anal verge. Thrombosed external hemorrhoids are mainly caused by the lateral expansion force and downward thrust of feces on the soft tissues of the anal canal, resulting in crushing injuries; sometimes accompanied by pushing and pulling injuries. Bleeding from ruptured blood vessels under the anal verge due to increased abdominal pressure is another form. The clinical manifestations are divided into two basic forms: (1) simple thrombosis due to ruptured blood vessels caused by simple crush injuries, which are not accompanied by edema. (2) Rupture of a vessel caused by pushing, pulling, and crushing, with impaired circulation, manifesting as both thrombosis and edema. Therefore, the procedure can be divided into simple thrombus stripping and external stripping and internal ligation according to the kinetic factors.
1.1.2 Vascular lagging external hemorrhoids (varicose external hemorrhoids)
The soft tissue at the anal canal is squeezed by feces, causing the subcutaneous veins at the anal verge to flex and deform, and the resulting soft mass is called vascular lagging external hemorrhoid. This type of external hemorrhoid is the result of the combined effect of the dilatory and pushing forces of feces over a long period of time. It has no further clinical significance until it causes an anal kinetic disorder.
1.1.3 Inflammatory external hemorrhoids
A fecal abrasion of the perianal skin, causing protrusion of skin folds at the injury with acute inflammatory manifestations such as redness, swelling, heat and pain, is called inflammatory external hemorrhoids. Inflammatory external hemorrhoids are mainly caused by friction between feces and perianal skin, and it is a symptomatic external hemorrhoid that can be treated symptomatically.
1.1.4 Connective tissue external hemorrhoids
Connective tissue external hemorrhoids are formed by the infection of damaged anal skin and the proliferation of tissue cells fibrosis in the focal area after the inflammation subsides. External connective tissue hemorrhoids are the result of the long-term action of frictional and thrusting forces. If it does not affect defecation and there is no significant discomfort, it can be left untreated.
1.1.5 Relationship between external hemorrhoids
From the point of view of fecal kinetic factors of external hemorrhoid formation, the four types of external hemorrhoids are not independent of each other in a parallel relationship. Vascular lagging external hemorrhoids are the prodromal stage of the (2) form of thrombosed external hemorrhoids, or they can be considered as the external hemorrhoidal part of combined hemorrhoids (mixed hemorrhoids); while connective tissue external hemorrhoids are more like the formation of excess skin after the absorption of the (2) form of thrombosed external hemorrhoids. Inflammatory external hemorrhoids are the result of fecal abrasion of the skin. There is only one form of thrombosed external hemorrhoid that is truly therapeutic.
1.2 Internal hemorrhoids
The pathological hypertrophy and downward movement of the anal cushion caused by the extrusion, friction and pushing down of feces is called internal hemorrhoids. The injuries formed by feces to the anal cushion are abrasion, pushing and pulling, and extrusion, and the three types of injuries cause pathological hypertrophy, downward displacement, and thrombosis of the anal cushion.
The submucosal muscle of the anal canal (Treitz muscle), which is a mixture of collagen fibers, elastic fibers, and smooth muscle fibers, has the following functions (1) to wrap around the internal hemorrhoidal vessels in a mesh pattern, forming a scaffold for the hemorrhoidal veins and supporting and fixing the anal cushion; (2) to attach to the skin of the pectineal area below the dentate line, forming the Parks ligament and fixing the anal canal. The function of this muscle is to retract the mucosa after defecation and prevent the mucosa and anal cushion from slipping out. Therefore, if any factor destroys the Treitz muscle, the submucosal connective tissue of the anal canal, causing relaxation and rupture of the Treitz muscle and elongation and hypertrophy of the Parks ligament, the anal cushion loses its support and slips downward. Various factors cause Treitz muscle abnormalities not only make the anal cushion lose support, but also release the restraint of the hemorrhoidal vein, resulting in venous expansion, anal cushion congestion and hypertrophy; increased resistance of the anal canal during defecation, prompting the patient to force defecation, making congestion and prolapse more and more serious, resulting in the destruction of supporting tissue intensified, hemorrhoids can develop from intermittent prolapse to continuous prolapse. Some of the persistent prolapsed hemorrhoids stimulate the internal sphincter muscle to cause spasm, coupled with the squeezing and pushing of feces on the prolapsed hemorrhoids, causing obstruction of hemorrhoidal venous blood return – thrombosis. The three anal pads are located in the truncated position at 3, 7, and 11 points, for the left 1 and right 2; the rectal canal is not a straight up and down funnel, the physiological state of the left and right sides are not subject to the same thrust and/or impact force, the right side is greater than the left, especially at 11 points the anal pad is subject to the greatest force. Therefore, internal hemorrhoid prolapse at 11 o’clock is the most common, and relaxation of the right side of the anal canal is more common than relaxation of the left side.
From a kinetic point of view, the current four-stage division of internal hemorrhoids has little clinical significance.
1.3 Relationship between internal and external hemorrhoids
Internal and external hemorrhoids can exist independently or in combination due to differences in location and forces. Some of the internal hemorrhoids can form external hemorrhoidal parts in the area below the dentate line due to the extrusion and downward pushing of feces.
1.4 Combined hemorrhoids (mixed hemorrhoids)
The hemorrhoids are located in the same orientation above and below the dentition line and become a whole, and both internal and external hemorrhoids are present, which is called combined hemorrhoids (mixed hemorrhoids). Combined hemorrhoids are caused by abrasions, pushing and pulling injuries, and crushing injuries formed by feces on the soft tissues of the anal canal and rectum.
The Treitz muscle and its downward extending Parks ligament and joint longitudinal muscle together form a three-dimensional mesh around the rectum of the anal canal; the Parks ligament is attached to the migrating epithelium of the anal canal and the joint longitudinal muscle to the perianal skin. When the force of feces on the anal cushion and the skin of the anal canal is too large or too frequent, the fibrous tissue of the reticular structure will relax and break, the anal cushion will lose its support and slip, and the migrating epithelium of the anal canal and the perianal skin will relax. The subluxation of the slipped anal cushion and the loose perianal skin of the anal canal as well as the thrombus and edema below the dentate line form a pathologically high resistance state at the anal outlet, which already affects the smooth elimination of feces, or causes a certain degree of anal kinetic disorder.
Surgical treatment of combined hemorrhoids is commonly performed with external stripping and internal ligation, and this procedure is more consistent with the requirement to eliminate or reduce anorectal kinetic disorders. The surgical design of circumferential combined hemorrhoids (mixed hemorrhoids) is more reasonable in the experience of the Department of Anorectal Medicine of Nanjing Hospital – the postoperative procedure enables smooth fecal expulsion and less affects the anal self-control function. The method is (1) rational design: the three mother hemorrhoid areas are used as the focus for designing the peeling area. (2) Tooth-shaped separation: the three ligature points are not in the same plane. (3) Appropriate decompression: the base of the ligated internal hemorrhoid should not be too much and too large to avoid reducing more of the internal diameter of the anal canal. (4) Postoperative reset: return the ligated part to the anus after surgery to reduce the outlet resistance.
2.Fecal dynamics factors
The effect on anal fissures Anal fissures are lacerations or fissures in the anal canal or anal margin [9]. According to the direction of fecal force on the soft tissues of the anal canal, anal fissures can be divided into three categories from the perspective of anal dynamics: (1) classical anal fissures; (2) fissures of hemorrhoidal origin; and (3) mixed anal fissures.
2.1 Classical anal fissure
It refers to a total fracture of the epithelium of the anal canal located in the posterior median line or/and anterior median line on the surface of the internal anal dilator muscle. It has a typical anal pain cycle and in chronic cases a triad or quintuple fissure ulcer. This is caused by excessive fecal dilatation forces on the horizontal direction of the anal canal.
The combined force of the horizontal dilating force of the harder stool on the anal canal acts on the anterior and posterior sides of the canal, causing a full epithelial split at the posterior midline or/and anterior midline, and the stool repeatedly stimulates the exposed internal dilator muscle, causing spasm of the internal dilator muscle, which aggravates constipation, which in turn aggravates the spasm of the internal dilator muscle. So repeatedly, forming a vicious circle.
The treatment starts from two aspects, one is to adjust the diet, soften the stool, and reduce the squeezing and dilating force of the fecal mass on the anal canal. The second is to dilate the anal canal and make it larger in diameter through surgery or instruments, so that the stool can be expelled smoothly.
The surgery is performed by lateral partial internal sphincterotomy or posterior partial internal sphincterotomy. Under epidural, sacral, or subarachnoid anesthesia, the anus is fully relaxed, and if it cannot pass two fingers smoothly, there is an anal dynamics disorder.
2.2 Hemorrhoidogenic fissure
This refers to a fracture of the anal canal skin corresponding to the vicinity of the three main hemorrhoid areas. This fissure is not a full-length fissure of the anal canal skin and is often associated with prolapsed internal hemorrhoids. It is associated with a short period of anal pain after defecation, which is much less severe than the periodic anal pain of classic fissures and is partially manifested by a longer period of discomfort in the anal region after defecation. Unlike classic fissures, hemorrhoidal fissures are caused by the downward thrust or/and impact of feces on the anal cushion and are push-pull injuries to the skin of the anal canal, which are more superficial and do not stimulate the internal dilator muscle to cause spasm.
This type of anal fissure is mainly treated surgically by stripping the prolapsed internal hemorrhoids and changing the abnormal forces on the anal canal to achieve a dynamic balance of mechanics at the exit.
2.3 Mixed type of anal fissure
The clinical manifestations and signs of the above two types of anal fissures are present, and one or more anal canal skin fissures are present. Surgery is performed by external stripping and internal ligation and partial internal sphincterotomy.
3. Conclusion
In conclusion, there are many factors that influence the formation of hemorrhoids and anal fissures, including abnormal stool kinetics on the one hand and the anatomy of the soft tissue at the anal canal on the other. The kinetic abnormalities at the exit caused by the change of the nature and frequency of feces may dominate; the dynamic fecal forces on the rectum of the anal canal are friction, dilatation and thrust, and these three forces with different points of action and directions cause four kinds of injuries at the rectum of the anal canal: abrasion of the skin of the anal canal, crush injury of the soft tissues of the anal canal, fracture of the skin of the anal canal and push and pull injury of the skin of the anal canal. The four types of injuries form a state of high resistance at the anorectal outlet. The aim of treatment is mainly to change the abnormal forces on the anal canal so that feces can pass smoothly to achieve a dynamic balance of mechanics at the exit. The classification of anal fissures by kinetic principles is a guide to the choice of procedure for anal fissures.